Learning HTTP/2

Length = the first three bytes
Read the payload based on the length.
Take the appropriate action based on the frame type.
end loop
This is much simpler to write and maintain. It also has a second extremely significant
advantage over HTTP/1’s delimited format. Go back now and see if you see it as it is
core to one of HTTP/2’s key benefits. With HTTP/1 you need to send a complete
request or response before you can send another. Because of HTTP/2’s framing,
request and responses can be interwoven, or multiplexed. Multiplexing helps get
around problems such as head of line blocking which was described in section XXX.
For a description of all frames please see Appendix A.
Table 3-2. HTTP/2 Frame Types
Name ID Description
DATA 0x0 Carries the core content for a stream
HEADERS 0x1 Contains the HTTP headers and optionally priorities
PRIORITY 0x2 Indicates or changes the stream priority and dependencies
RST_STREAM 0x3 Allows an end point to end a stream (generally an error case)
SETTINGS 0x4 Communicates connection level parameters
PUSH_PROMISE 0x5 Indicates to a client that a server is about to send something
PING 0x6 Test connectivity and measure round trip time (RTT)
GOAWAY 0x7 Tells an end point that the peer is done accepting new streams
WINDOW_UPDATE 0x8 Communicates how many bytes an end point is willing to receive ( used for flow control )
CONTINUATION 0x9 Used to extend HEADER blocks.
Room for Extension
HTTP/2 built in the ability to handle new frame types called extension frames. This
provides a mechanism for client and server implementors to experiment with new
frame types without having to create a whole new protocol. Since by specification any
frame that is not understood by a consumer must be discarded, new frames on the
wire should not affect the core protocol. Of course, if your application is reliant on a
new frame and a proxy in the middle is dropping that frame then you might run into
a few problems…
Streams
The HTTP/2 specification defines a stream as “an independent, bidirectional
sequence of frames exchanged between the client and server within an HTTP/2 connection.”
You can think of a stream as a series of frames making up an individual
30 | Chapter 3: The Protocol